Charles Oman 
A History of England – Illustrated Edition – 1902 [EPUB ebook] 

In the dim dawn of history our island was a land of wood and marsh, broken here and there by patches of open ground, and pierced by occasional track-ways, which threaded the forest and circled round the edges of the impassable fen. The inhabited districts of the country were not the fertile river-bottoms where population grew thick in after-days; these were in primitive times nothing but sedgy water-meadows or matted thickets. Men dwelt rather on the thinly wooded upland, where, if the soil was poor, it was at any rate free from the tangled undergrowth that covered the valleys. It was on the chalk ridges of Kent or Wilts, or the moorland hills of Yorkshire or Cornwall, rather than on the brink of the Thames or Severn, that the British tribes clustered thick. Down by the rivers there were but small settlements of hunters and fishers perched on some knoll that rose above the brake and the rushes.